Interconnect structure that controls spacing between a probe card and a contact substrate

ABSTRACT

One embodiment of the present invention is a structure useful for testing circuits that includes: (a) a substrate having contactors on a first side and pads on a second side; (b) a card having pads on a first side; and (c) interconnectors that electrically connect the pads on the second side of the substrate with the pads on the card; wherein at least one of the interconnectors includes at least a portion that does not melt at temperatures in a range from about 183° C. to about 230° C., and the distance between the substrate and the card is determined by a dimension of the at least a portion.

This is a divisional of U.S. patent application Ser. No. 10/418,512,filed Apr. 16, 2003, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/387,216, filed on Mar. 12, 2003. This patentdocument is also related to U.S. patent application Ser. No. 10/386,875,which was filed on Mar. 12, 2003. All of these prior applications arehereby incorporated by reference in their entirety.

TECHNICAL FIELD OF THE INVENTION

One or more embodiments of the present invention pertain to: (a) one ormore structures useful, for example and without limitation, for testingcircuits, for example and without limitation, integrated circuits(“ICs”) at a wafer level; and (b) one or more methods for fabricatingsuch structures.

BACKGROUND OF THE INVENTION

As is known, a substrate (sometimes also referred to in the art as aninterposer) is a device that provides a fan-out between I/O (i.e.,electrical inputs and outs) of a circuit, for example and withoutlimitation, an integrated circuit (“IC”) and a Probe Card to enabletesting of the IC, for example, at a wafer level. Such a substrate maybe a rigid substrate, a semi-flex substrate, a flex substrate, and soforth, and such substrates often have a relatively low cost whencompared to that of the Probe Card.

As IC geometries have decreased in size dramatically since such deviceswere first introduced several decades ago, so too have geometriesassociated with wiring connections to their I/O. For example, presentdesigns include the use of bumped wafer pad pitches of 200 μm or less.In order to test such ICs, one is required to utilize high densityinterconnect (“HDI”) substrates having matching fine connector pitches.

Substrates available today, and the manner in which they are used, areproblematic for two basic reasons. First, manufacturing techniques usedto fabricate such substrates and to connect them to Probe Cardstypically require multiple expensive steps. Second, if one of theconnectors on the substrate gets damaged, it cannot be replaced, for themost part, or is difficult or expensive to rework. In addition, wheneverthe substrate wears out, or gets damaged, one typically has to throwaway the Probe Card together with the substrate. In particular, this isbecause, due to manufacturing techniques used to fabricate suchsubstrates and to connect them to Probe Cards, it is a prohibitivelylengthy and costly process to separate the substrate from the ProbeCard.

In light of the above, there is a need in the art for: (a) one or morestructures useful, for example and without limitation, for testingcircuits, for example and without limitation, ICs at a wafer level thatsolve one or more of the above-identified problems; and (b) one or moremethods for fabricating such structures.

SUMMARY OF THE INVENTION

One or more embodiments of the present invention satisfy one or more ofthe above-identified needs in the art. In particular, one embodiment ofthe present invention is a structure useful for testing circuits thatcomprises: (a) a substrate having contactors on a first side and pads ona second side; (b) a card having pads on a first side; and (c)interconnectors that electrically connect the pads on the second side ofthe substrate with the pads on the card; wherein at least one of theinterconnectors includes at least a portion that does not melt attemperatures in a range from about 183° C. to about 230° C., and thedistance between the substrate and the card is determined by a dimensionof the at least a portion.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross sectional view that shows a pinalignment fixture usedto connect a substrate to a Probe Card in accordance with one or moreembodiments of the present invention prior to re-flow;

FIG. 1A is a cross sectional view that shows a stiffening mechanismconnected to a Probe Card in accordance with one or more embodiments ofthe present invention;

FIG. 1B is a bottom view that shows the stiffening mechanism shown inFIG. 1A;

FIG. 2 is a top view that shows a portion of a flex substrate that isfabricated in accordance with one or more embodiments of the presentinvention;

FIGS. 3-5 are cross sectional views that show substrates which havebevels formed on the edges of the substrates that have been fabricatedin accordance with one or more embodiments of the present invention;

FIG. 6 shows a clamp mechanism that is fabricated in accordance with oneor more embodiments of the present invention;

FIG. 7 is a cross sectional view that shows a chip substrate that isfabricated in accordance with one or more embodiments of the presentinvention;

FIG. 8 shows a Pogo pin used to fabricate one or more embodiments of thepresent invention;

FIG. 9 is a top perspective view that shows a connector-holder bottomplate that is fabricated in accordance with one or more embodiments ofthe present invention;

FIG. 10 is a bottom perspective view that shows a connector-holder topplate that is fabricated in accordance with one or more embodiments ofthe present invention;

FIG. 11 is a cross sectional view that shows a hole in theconnector-holder bottom plate shown in FIG. 9;

FIG. 12 is a cross sectional view that shows a hole in theconnector-holder top plate shown in FIG. 10;

FIG. 13 is an exploded view that shows a portion of a structure used totest circuits that is fabricated in accordance with one or moreembodiments of the present invention;

FIG. 14 is a cross sectional view that shows a groove cut into a side ofa substrate that is fabricated in accordance with one or moreembodiments of the present invention;

FIG. 15 is a top view of a clamp that is fabricated in accordance withone or more embodiments of the present invention;

FIG. 16 is a cross sectional view that shows a structure for testingcircuits that is fabricated in accordance with one or more embodimentsof the present invention;

FIG. 17 is a top view that shows a substrate and an RF interface boardthat are used in the structure shown in FIG. 16; and

FIG. 18 is a cross sectional view of a structure that is fabricated inaccordance with one or more embodiments of the present invention.

DETAILED DESCRIPTION

As is known, circuits such as, for example and without limitation,integrated circuits (“ICs”), are fabricated on wafers, and the circuitsare tested by applying electrical signals to circuit inputs andanalyzing electrical signals produced at circuit outputs (such circuitinputs and outputs may be bumped or not). As is also known, a Probe Cardthat provides an interface between the circuit inputs and outputs(“I/O”) on the wafer and a Tester is used to perform such testing.

As the density of I/O of ICs has increased, it has become common toconnect the Probe Card to a substrate (sometimes referred to in the artas an interposer) having an array of contactors (for example and withoutlimitation, 12-50 μm high structures that are sometimes also referred toin the art as posts) on a top or testing side (i.e., a side thatcontacts the IC on the wafer) and having a ball grid array (“BGA”) ofpads on a bottom side (i.e., a side that contacts the Probe Card). Thecontactors are wired through the substrate, and each wire ends at a padin the BGA on the bottom side of the substrate. The array of contactorshas a pitch and density (sometimes referred to as a footprint) thatmatches that of the IC, and the BGA has a pitch and density that matchesthat of the Probe Card. Substrates used to test present and future ICs,may be high density interconnect (“HDI”) substrates where the pitch ofthe array of contactors could be as small as 125 μm or less. Thus, oneor more embodiments of the present invention relate to methods forassembling a structure used to test circuits, for example and withoutlimitation, ICs, whether bumped or not, on a wafer, and one or morefurther embodiments relate to the assembled structure itself.

In particular, one or more embodiments of the present invention aremethods for connecting a substrate, for example and without limitation,a rigid substrate, a flex substrate, a semi-flex substrate, asilicon/glass substrate (for example and without limitation, asilicon/glass structure that includes MEMS-type spring contactors), andso forth, to a Probe Card to provide structures that are used, forexample and without limitation, to test circuits, for example andwithout limitation, integrated circuits (“ICs”), whether bumped or not,on a wafer. Advantageously, in accordance with one or more embodimentsof the present invention, structures are produced that may be used costeffectively for testing because, among other reasons, such substratesmay be replaced easily and rapidly with a new ones whenever thesubstrates are damaged or worn. In addition, advantageously, inaccordance with one or more embodiments of the present invention,structures are produced having a relatively short distance between thesubstrate and the Probe Card, whereby electrical connections between thesubstrate and the Probe Card have better electrical properties thanthose of structures produced using prior art methods.

The following describes a method (“Method I”) for connecting a substrateto a Probe Card (i.e., for connecting BGA pads of a substrate to BGApads of a Probe Card) in accordance with one or more embodiments of thepresent invention, which substrate can be, for example and withoutlimitation, a rigid substrate, a flex substrate, or a semi-flexsubstrate. FIG. 1 is a cross sectional view that shows a pinalignmentfixture used to carry out Method I prior to re-flow.

As shown in FIG. 1, the pinalignment fixture includes base plate 100.Base plate 100 is, for example and without limitation, an aluminum baseplate, a Durostone® composite material base plate, or a base plate thatis fabricated using any one of a number of other materials that are wellknown to those of ordinary skill in the art, which materials arerelatively stable at processing temperatures of subsequent steps ofMethod I. In accordance with one or more embodiments of the presentinvention, base plate 100 has an area of about the same size as that ofProbe Card 130, and base plate 100 has a thickness in a range, forexample and without limitation, from about 5.0 mm to about 7.0 mm. Asfurther shown in FIG. 1, the pinalignment fixture includes alignmentpins that are affixed to base plate 110 such as alignment pins 120 and121. In accordance with one or more embodiments of the presentinvention, the alignment pins have a diameter in a range, for exampleand without limitation, from about 0.7 mm to about 1.1 mm diameter. Asone can readily appreciate, the pinalignment fixture may include, forexample and without limitation, three (3) or four (4) such alignmentpins.

In a first, optional step of Method I, release film 110 such as, forexample and without limitation, a Mylar film or a Teflon film, isaligned with, and placed over, base plate 100 of the pinalignmentfixture (holes in release film 110 match the positions of the alignmentpins such as pins 120 and 121). Next, Probe Card 130 is aligned with,and placed over, release film 110 on the pinalignment fixture (holes inProbe Card 130 match the positions of the alignment pins such as pins120 and 121). Vias 141 and 142 are formed in a commercially available“interconnector alignment” film such as, for example and withoutlimitation, polyimide film 150 having adhesive (not shown) (for exampleand without limitation, epoxy, acrylic, epoxy-acrylic, and so forth) onone, or both, side(s), and a release film (not shown) (for example andwithout limitation, a Mylar film or Teflon film) disposed on theadhesive side. Vias 141 and 142 may be formed in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art such as, for example and without limitation, by drilling,punching, lasing, and so forth. The locations of vias 141 and 142 inpolyimide film 150 match the locations of BGA pads 131 and 132,respectively, on the top side of Probe Card 130. Although not shown assuch in FIG. 1, the cross sectional area of vias 141 and 142 istypically larger that the cross sectional areas of pads 131 and 132,respectively. As one can readily appreciate, the step of fabricating theinterconnector alignment film (i.e., polyimide film 150) may take placeat any time before it is needed to be placed in use. Next, polyimidefilm 150 is aligned with, and placed over, Probe Card 130 on thepinalignment fixture (holes in polyimide film 150 match the positions ofthe alignment pins such as pins 120 and 121). Next, weight 210, forexample, an aluminum or stainless steel plate having a thickness in arange, for example and without limitation, from about 10 mm to about12.7 mm, and having an area of about the same size as that of Probe Card130 is aligned with, and placed over polyimide film 150 on thepinalignment fixture to apply pressure to polyimide film 150 (holes inplate 210 match the positions of the alignment pins such as pins 120 and121). Next, polyimide film 150 is laminated to Probe Card 130 by, forexample and without limitation, baking in an oven. The oven temperatureis in a range, for example and without limitation, from about 150° C. toabout 200° C., the pressure exerted by the weight of plate 210 is in arange, for example and without limitation, from about 14 kg/cm² to about28 kg/cm², and the time spent in the oven is in a range, for example andwithout limitation, from about 1 hour to about 2 hours. Next, weight 210is removed.

Next, vias 141 and 142 are filled with paste 171 and 172, respectively,using, for example and without limitation, the release film of polyimidefilm 150 as a mask. Paste 171 and 172 may be any one of a number ofconductive pastes that are well known to those of ordinary skill in theart such as, for example, and without limitation, a Ag conductive paste,a Au conductive paste, a Cu conductive paste, and so forth, or it may beany one of a number of solder pastes that are well known to those ofordinary skill in the art. Paste 171 and 172 may be applied utilizingany one of a number of methods that are well known to those of ordinaryskill in the art such as, for example and without limitation, methodsutilizing a dispensing machine, methods utilizing screen-printing,methods utilizing a squeegee, and so forth. Also, in accordance with oneor more further embodiments of the present invention, paste 171 and 172can be a compliant, conductive paste. Such a compliant conductive pastemay be any one of a number of such products that are well known to thoseof ordinary skill in the art such as, for example and withoutlimitation, an elastomer such as a silicone elastomer having conductiveparticles embedded therein. The use of a compliant conductive paste maybe advantageous in that the resulting structure (sometimes referred toas a “lay-up”) may be able to take up vertical movements or movements ina Z-direction caused during testing by non-planarity of contactors onthe substrate, pads on the substrate, pads on the Probe Card, and/or I/Ocontacts on the wafer. Next, the release film is removed.

Next, a stencil (sometimes referred to in the art as a solder ballstencil—not shown) that is fabricated in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart is aligned with, and placed, over polyimide film 150 on thepinalignment fixture (holes in the stencil match the positions of thealignment pins such as pins 120 and 121); the edges of the stencil couldhave a corral formed thereon, for example, a corral of tape, to trapballs within the confines of the stencil. The holes in the stencil areslightly larger than the largest cross section of interconnectors, forexample and without limitation, balls (described below), so theinterconnectors, for example and without limitation, balls, will fallthrough the holes in the stencil when the stencil is removed. Inaccordance with one or more embodiments of the present invention, balls181 and 182 shown in FIG. 1 are comprised of a rigid core, for exampleand without limitation, a solid copper (Cu) core, and a coating, forexample and without limitation, a solder coating such as, for exampleand without limitation, a eutectic solder coating. Next, balls 181 and182 are placed over the stencil, and the stencil is removed. Thediameter of the core of balls 181 and 182 is in a range, for example andwithout limitation, from about 5 mils to about 10 mils, and the coatinghas a thickness in a range, for example and without limitation, fromabout 20 μm to about 25 μm. The diameter of the core of balls 181 and182 ought to be larger than the thickness of polyimide film 150 so thatthe core of balls 181 and 182 can contact pads 191 and 192,respectively, on substrate 190 and pads 131 and 132, respectively, onProbe Card 130.

Next, substrate 190 (for example and without limitation, a rigidsubstrate, a flex substrate, a semi-flex substrate, and so forth) isaligned with, and placed over balls 181 and 182 on the pinalignmentfixture (holes in substrate 190 match the positions of the alignmentpins such as pins 120 and 121). Next, optional release film 200, forexample and without limitation, a Mylar or Teflon film, is aligned with,and placed over, structure 190 (and contactors 195 and 196) on thepinalignment fixture 1000 (holes in release film 200 match the positionsof the alignment pins such as pins 120 and 121, for example and withoutlimitation, release film 200 may have a cut-out region where the cut-outregion includes an area in which the contactors are disposed so thatthey are not damaged during re-flow). Next, weight 210 is aligned with,and placed over, release film 200 on the pinalignment fixture 1000 toapply pressure. Next, the solder coating on balls 181 and 182 isre-flowed, for example and without limitation, by baking in an oven at atemperature in a range, for example and without limitation, from about200° C. to about 230° C. Advantageously, polyimide film 150 holds balls181 and 182 in place during the re-flow, and it helps support each ballduring testing. During the re-flow process, weight 210 provides a forcethat causes the solder to flow so that the distance between substrate190 and Probe Card 130 is determined by a dimension of the core of balls181 and 182, for example and without limitation, the diameter of a Cucore of balls 181 and 182 (it should be understood that other mechanismsfor applying such a force may be used to fabricate one or more furtherembodiments of the present invention such as, for example and withoutlimitation, by the use of springs that are adapted to urge substrate 190and Probe Card 130 towards each other). Thus, the rigid core of balls181 and 182 acts as a stopper to vertical displacement of substrate 190relative to Probe Card 130. Since three (3) points determined a plane,the plane of substrate 190 will be determined substantially by thediameter of the three largest cores (where the core diameters areexpected to vary due to manufacturing tolerances). Advantageously,Method I provides a structure wherein a plane of substrate 190 issubstantially parallel to a plane of Probe Card 130. Finally, thestructure or lay-up comprised of connected substrate 190 and Probe Card130 is removed from the pinalignment fixture, and release films 110 and200 are removed.

In accordance with one or more further embodiments of the presentinvention, a stiffening mechanism is connected to a side of the ProbeCard opposite from the side to which the substrate is connected. FIG. 1Ais a cross sectional view that shows how stiffening mechanism 447 isconnected to Probe Card 457 in accordance with one or more embodimentsof the present invention, and FIG. 1B is a bottom view that showsstiffening mechanism 447. As shown in FIG. 1A, stiffening mechanism 447is connected to Probe Card 457 so that substrate 467 is encompassedwithin an area delineated by the perimeter of stiffening mechanism 447.As further shown in FIG. 1A, the area delineated by the perimeter ofstiffening mechanism 447 does not include electrical contacts 477disposed on Probe Card 457, which electrical contacts 477 provideelectrical connections between Probe Card 457 and a test interfacesystem.

As shown in FIG. 1A, stiffening mechanism 447 includes leg structure 451that is used to connect ring structure 448 (shown in FIG. 1B) to ProbeCard 457 at a multiplicity of locations about the periphery ofstiffening mechanism 447. Leg structure 451 may comprise, for exampleand without limitation, a number of legs, leg structure 451 may be aring, and so forth. Stiffening mechanism 447 is connected to Probe Card557 using a connection mechanism such as, for example and withoutlimitation, screws and nuts. Also, in accordance with one or morealternative such embodiments, ring structure 448 shown in FIG. 1B mayfurther include supports such as radial arms, struts, ribs, and thelike. In accordance with one or more further embodiments of the presentinvention, stiffening mechanism 447 may be comprised of a solid plate,with or without a leg structure like leg structure 451 described above.Lastly, stiffening mechanism 447 may be fabricated from any one of anumber of materials such as, for example and without limitation, as ametal, a plastic, a ceramic, and so forth. Advantageously, in accordancewith such embodiments of the present invention, stiffening mechanism 447provides support for substrate 467 during testing.

It should be understood by those of ordinary skill in the art that balls181 and 182 utilized in the above-described embodiment of the presentinvention are interconnectors that provide electrical continuity betweenpads on the bottom or non-testing side of the substrate and pads on thetop side of the Probe Card. In general, the interconnectors may be anytype of electrical conductor (for example and without limitation, it iscomprised of an electrical conducting material): (a) whose electricalconductivity is sufficient to satisfy design electrical requirements ofa resulting structure or lay-up; and (b) that has at least a core thatdoes not melt as a result of applying heat during the fabricationprocess. For example and without limitation, the core does not melt attemperatures used to re-flow eutectic solder (for example, temperaturesin a range from about 183° C. (the melting point of eutectic solder) toabout 230° C.). Thus, for this case, for example, and withoutlimitation, the core may be a material that melts at a temperature thatis higher than 230° C. since such a material would not melt in thespecified range. In light of this, when the interconnectors are embodiedas balls, such balls may be: (a) solid Cu balls; (b) solid Cu balls thatare coated with eutectic solder; (c) solid Indium alloy balls; (d) solidIndium alloy balls that are coated with solder; (e) solid high leadsolder (for example and without limitation, 97/3 or 95/5) balls; (f)solid high lead solder (for example and without limitation, 97/3 or95/5) balls that are coated with solder; and (g) so forth. In addition,further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) is notsolid, and further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) comprises aceramic material that is embedded with a conducting material such as,for example, and without limitation, gold, Cu, silver, Indium, Ni, andso forth. Embodiment of such balls may be fabricated in accordance withany one of a number of methods that are well known to those of ordinaryskill in the art, and one or more embodiments of such balls arecommercially available.

In accordance with one or more further embodiments of the presentinvention, the interconnectors may be compliant conductive balls, forexample and without limitation, compliant conductive plastic balls. Forexample, suitable conductive, compliant balls are commercially availablethat have a plastic core (for example and without limitation, a plasticcore having a hollow center), which plastic core is surrounded or coatedwith: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) alayer of Cu, a layer of Ni, and a layer of Au; (d) one or more of alayer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. Inaddition, in accordance with one or more still further embodiments ofthe present invention, the interconnectors may be springs (suitablesprings may be obtained commercially). Advantageously, in accordancewith one or more such embodiments of the present invention, suchcompliant, conductive balls may compress when the structure is used in aTester and, thereby, the compliant, conductive balls may be able make upfor any non-planarity of the structure as a whole.

It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to thesubstrate and to the Probe Card utilizing any one of a number of methodsthat are well known to those of ordinary skill in the art. For exampleand without limitation, if an interconnector is embodied as a soldercoated Cu ball, such a solder coated ball may be affixed: (a) byre-flow; (b) by re-flow after applying flux to the substrate and/or theProbe Card; (c) by re-flow after applying conductive paste to thesubstrate and/or the Probe Card; (d) by re-flow after applyingconductive paste to the substrate or the Probe Card and applying flux tothe Probe Card or the substrate, respectively; (e) and so forth. As afurther example, if an interconnector is embodied as a Cu ball or as aconductive, compliant ball such as that described above, such a ball maybe affixed: (a) by re-flow after applying solder paste to the substrateand the Probe Card; (b) by curing after applying conductive paste to thesubstrate and the Probe Card; (c) by re-flow after applying conductivepaste to the substrate or the Probe Card and applying solder paste tothe Probe Card or the substrate, respectively; (d) and so forth. As astill further example, if the interconnector is embodied as a spring,such a spring may be affixed: (a) by re-flow after applying solder pasteto the substrate and the Probe Card; (b) by curing after applyingconductive paste to the substrate and the Probe Card; (c) by re-flowafter applying conductive paste to the substrate or the Probe Card andapplying solder paste to the Probe Card or the substrate, respectively;(d) and so forth.

In accordance with one or more still further embodiments of the presentinvention, the interconnectors may be eutectic solder balls that areaffixed by curing after applying conductive paste to the substrate andthe Probe Card. For example, such a curing step will occur attemperatures in a range, for example and without limitation, from about120° C. to about 160° C., which range of temperatures is below themelting temperature (˜183° C.) of eutectic solder. Thus, in accordancewith such still further embodiments of the present invention, theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process. Further, as was explained above, because theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process, the distance between the substrate and theProbe Card may be determined by the size of the eutectic solder balls.

It should also be understood that further embodiments of the presentinvention exist wherein: (a) no interconnector alignment film is used;(b) an interconnector alignment film is applied to the Probe Card (seethe above-described embodiment where the interconnector alignment filmis embodied as polyimide film 150); (c) an interconnector alignment filmmay be applied to the substrate in a manner that will be readilyunderstood by one of ordinary skill in the art in light of thespecification; (d) and so forth.

In accordance with one or more embodiments of the present invention,when the interconnectors are short, structures fabricated utilizing suchinterconnectors have short interconnection distances from IC bumps undertest to the Probe Card. For example, when interconnectors are embodiedas balls such as balls 181 and 182 described above having a solid Cucore with a diameter in a range, for example and without limitation,from about 5 mils to about 10 mils, structures fabricated utilizing suchballs have interconnection distances from IC bumps under test to theProbe Card that are short. Advantageously, the resulting structures haveelectrical properties, such as, for example and without limitation, lineresistance, inductance, and so forth, that are improvements over similarelectrical properties for structures having longer interconnectiondistances.

An advantage provided by one or more of the above-described embodimentsof the present invention is that the substrate may be removed from theProbe Card when the substrate becomes worn or is damaged. For example,to do this, one would remove the Probe Card from a Tester, de-solder theworn or damaged substrate utilizing any one of a number of de-solderingmethods that are well known to those of ordinary skill in the art, andconnect a new substrate to the Probe Card in its place. For example andwithout limitation, such a de-soldering method may include the use offorced hot air (the temperature being above the melting point ofsolder), and a suction to retrieve the substrate when the solder hasmelted to a sufficient degree. The new structure may then be replaced inthe Tester.

The following describes another method (“Method II”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) in accordance with one or more embodimentsof the present invention wherein, in accordance with Part I of MethodII, interconnectors are connected to the substrate before the substrateis connected to the Probe Card, which substrate can be, for example andwithout limitation, a rigid substrate, a flex substrate, or a semi-flexsubstrate.

In a first, optional step of Part I of Method II, a release film (suchas, for example and without limitation, a release film like thatdescribed above in conjunction with Method I) is aligned with, andplaced over, a base plate of a pinalignment fixture (such as, forexample and without limitation, a base plate and a pinalignment fixturelike those described above in conjunction with Method I). Next, asubstrate is aligned with, and placed over, the release film on thepinalignment fixture with its BGA pad side up. Next, a paste stencilmask that is fabricated in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art isaligned with, and placed over, the substrate on the pinalignmentfixture. Next, a paste such as, for example and without limitation, aflux or a no-clean solder paste is applied onto the BGA pads of thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art such as, for example and withoutlimitation, methods utilizing a dispensing machine, methods utilizingscreen-printing, methods utilizing a squeegee, and so forth. Also, inaccordance with one or more further embodiments of the presentinvention, the paste may be any one of a number of conductive pastesthat are well known to those of ordinary skill in the art such as, forexample, and without limitation, a Ag conductive paste, a Au conductivepaste, a Cu conductive paste, and so forth, or it may be any one of anumber of solder pastes that are well known to those of ordinary skillin the art. Further, the paste can be a compliant, conductive pastewhere such compliant conductive paste may be any one of a number of suchproducts that are well known to those of ordinary skill in the art suchas, for example and without limitation, an elastomer such as a siliconeelastomer having conductive particles embedded therein. The use of acompliant conductive paste may be advantageous in that the resultingstructure may be able to take up vertical movements or movements in aZ-direction caused during testing by non-planarity of contactors on thesubstrate, pads on the substrate, pads on the Probe Card, and/or I/Ocontacts on the wafer. Next, the paste stencil mask is removed.

Next, a stencil (such as, for example and without limitation, a stencillike that described above in conjunction with Method I to positionballs) is aligned with, and placed over, the substrate on thepinalignment fixture; the edges of the stencil could have a corralformed thereon (such as, for example and without limitation, a corrallike that described above in conjunction with Method I). Next, ballshaving a rigid core and a solder coating (such as, for example andwithout limitation, balls like those described above in conjunction withMethod I) are placed over the stencil, and the stencil is removed. Next,the solder coating on the balls is re-flowed (in a re-flow step such as,for example and without limitation, a re-flow step like that describedabove in conjunction with Method I). The resulting piece may beinspected, and re-work may take place if necessary. As one can readilyappreciate from the above, Part I of Method II may be utilized, amongother things, to prepare a replacement substrate for connection to aProbe Card by affixing balls to the BGA pads thereof.

It should be understood by those of ordinary skill in the art that theballs utilized in the above-described embodiment of the presentinvention are interconnectors that provide electrical continuity betweenpads on the bottom or non-testing side of the substrate and pads on thetop side of the Probe Card. In general, the interconnectors may be anytype of electrical conductor (for example and without limitation, it iscomprised of an electrical conducting material): (a) whose electricalconductivity is sufficient to satisfy design electrical requirements ofa resulting structure or lay-up; and (b) that has at least a core thatdoes not melt as a result of applying heat during the fabricationprocess. For example and without limitation, the core does not melt attemperatures used to re-flow eutectic solder (for example, temperaturesin a range from about 183° C. (the melting point of eutectic solder) toabout 230° C.). Thus, for this case, for example, and withoutlimitation, the core may be a material that melts at a temperature thatis higher than 230° C. since such a material would not melt in thespecified range. In light of this, when the interconnectors are embodiedas balls, such balls may be: (a) solid Cu balls; (b) solid Cu balls thatare coated with eutectic solder; (c) solid Indium alloy balls; (d) solidIndium alloy balls that are coated with solder; (e) solid high leadsolder (for example and without limitation, 97/3 or 95/5) balls; (f)solid high lead solder (for example and without limitation, 97/3 or95/5) balls that are coated with solder; and (g) so forth. In addition,further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) is notsolid, and further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) comprises aceramic material that is embedded with a conducting material such as,for example, and without limitation, gold, Cu, silver, Indium, Ni, andso forth. Embodiment of such balls may be fabricated in accordance withany one of a number of methods that are well known to those of ordinaryskill in the art, and one or more embodiments of such balls arecommercially available.

In accordance with one or more further embodiments of the presentinvention, the interconnectors may be compliant conductive balls, forexample and without limitation, compliant conductive plastic balls. Forexample, suitable conductive, compliant balls are commercially availablethat have a plastic core (for example and without limitation, a plasticcore having a hollow center), which plastic core is surrounded or coatedwith: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) alayer of Cu, a layer of Ni, and a layer of Au; (d) one or more of alayer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. Inaddition, in accordance with one or more still further embodiments ofthe present invention, the interconnectors may be springs (suitablesprings may be obtained commercially).

It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art. For example and withoutlimitation, if an interconnector is embodied as a solder coated Cu ball,such a solder coated ball may be affixed to the substrate: (a) byre-flow; (b) by re-flow after applying flux to the substrate; (c) byre-flow after applying conductive paste to the substrate; and (d) soforth. As a further example, if an interconnector is embodied as a Cuball or as a conductive, compliant ball such as that described above,such a ball may be affixed to the substrate: (a) by re-flow afterapplying solder paste to the substrate; (b) by curing after applyingconductive paste to the substrate; and (c) so forth. As a still furtherexample, if the interconnector is embodied as a spring, such a springmay be affixed to the substrate: (a) by re-flow after applying solderpaste to the substrate; (b) by curing after applying conductive paste tothe substrate; and (c) so forth.

It should also be understood that further embodiments of the presentinvention exist wherein: (a) no interconnector alignment film is used;or (b) an interconnector alignment film is applied to the substrate in amanner that will be readily understood by one of ordinary skill in theart in light of the specification.

The following describes Part II of Method II, i.e., a method forconnecting a structure having balls affixed to the BGA pads thereto tothe Probe Card. In a first, optional step of Part II of Method II, arelease film (such as, for example and without limitation, a releasefilm like that described above in conjunction with Method I) is alignedwith, and placed over, a base plate of a pinalignment fixture (such as,for example and without limitation, a base plate and a pinalignmentfixture like those described above in conjunction with Method I). Next,the Probe Card is aligned with, and placed over, the release film on thepinalignment fixture. Next, a paste stencil mask (such as, for exampleand without limitation, a paste stencil mask like that described abovein conjunction with Part I of Method II) is aligned with, and placedover the Probe Card on the pinalignment fixture. Next, a paste (such as,for example and without limitation, a paste like that described above inconjunction with Part I of Method II) is applied onto the pads of theProbe Card (in a paste application step such as, for example and withoutlimitation, a paste application step like that described above inconjunction with Part I of Method II). Next, the paste stencil isremoved.

Next, the substrate, with the balls facing down, is aligned with, andplaced over the Probe Card on the pinalignment fixture. Next, in anoptional step, a release film (such as, for example and withoutlimitation, a release film like that described above in conjunction withPart I of Method II) is aligned with, and placed over, the structure onthe pinalignment fixture. Next, a weight (such as, for example andwithout limitation, a weight like that described above in conjunctionwith Method I) is aligned with, and placed over, the release film on thepinalignment fixture. Next, the solder coating on the balls is re-flowed(in a re-flow step such as, for example and without limitation, are-flow step like that described above in conjunction with Part I ofMethod II). During the re-flow process, the weight provides a force thatcauses the solder to flow so that the distance between the substrate andthe Probe Card is determined by a dimension of the core of the balls(for example and without limitation, the diameter of the core). Itshould be understood that other mechanisms for applying a force (i.e.,other than the weight) that causes the solder to flow so that thedistance between the substrate and the Probe Card is determined by thediameter of the core of the balls may be used to fabricate one or morefurther embodiments of the present invention such as, for example andwithout limitation, by the use of springs that are adapted to urge thesubstrate and the Probe Card towards each other. Finally, the structureor lay-up comprised of the connected substrate and Probe Card is removedfrom the pinalignment fixture, and the release films are removed. In analternative embodiment of Part II of Method II, a support film such as,for example and without limitation, a polyimide film, may be placed overthe Probe Card before the paste is applied to help support the ballsduring testing. In addition, a stiffening mechanism like that describedabove may be (optionally) connected to a side of the Probe Card oppositefrom the side to which the substrate is connected.

It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to the ProbeCard utilizing any one of a number of methods that are well known tothose of ordinary skill in the art. For example and without limitation,if an interconnector is embodied as a solder coated Cu ball, such asolder coated ball may be affixed to the Probe Card: (a) by re-flow; (b)by re-flow after applying flux to the Probe Card; (c) by re-flow afterapplying conductive paste to the Probe Card; and (d) so forth. As afurther example, if an interconnector is embodied as a Cu ball or as aconductive, compliant ball such as that described above, such a ball maybe affixed to the Probe Card: (a) by re-flow after applying solder pasteto the Probe Card; (b) by curing after applying conductive paste to theProbe Card; and (c) so forth. As a still further example, if theinterconnector is embodied as a spring, such a spring may be affixed tothe Probe Card: (a) by re-flow after applying solder paste to the ProbeCard; (b) by curing after applying conductive paste to the Probe Card;and (c) so forth.

In accordance with one or more still further embodiments of the presentinvention, the interconnectors may be eutectic solder balls that areaffixed by curing after applying conductive paste to the substrate andthe Probe Card. For example, relevant curing steps will occur attemperatures in a range, for example and without limitation, from about120° C. to about 160° C., which range of temperatures is below themelting temperature (˜183° C.) of eutectic solder. Thus, in accordancewith such still further embodiments of the present invention, theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process. Further, as was explained above, because theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process, the distance between the substrate and theProbe Card may be determined by the size of the eutectic solder balls.

The following describes another method (“Method III”) for connecting astructure comprised of at least two substrates to a Probe Card (i.e.,for connecting BGA pads of the structure comprised of at least twosubstrates to BGA pads of the Probe Card) in accordance with one or moreembodiments of the present invention. Due to limitations in wiringdensity for substrates presently available in the market, for high I/Ochip applications (for example and without limitation, chip applicationsinvolving over 3,000 I/O connections) the wiring density may beinsufficient to wire all contactors from the top or testing surface of asubstrate through to the other side to pads that are to be connected toa Probe Card. Thus, for example and without limitation, in such high I/Ochip applications, a substrate having contactors that face a wafer mightbe fanned-out to another substrate that is sometimes referred to as asecond level substrate. Then, in accordance with one or more embodimentsof the present invention, a first substrate having contactors for use intesting a circuit is connected to a second substrate usinginterconnectors such as, for example and without limitation, any of theinterconnectors described above in conjunction with Methods I or II; andthe two substrates are connected utilizing any of the embodimentsdescribed above in conjunction with Method I or Method II. Next, thestructure comprised of the two substrates may be connected to the ProbeCard utilizing any of the embodiments described above in conjunctionwith Method I or Method II. In addition, a stiffening mechanism likethat described above may be (optionally) connected to a side of theProbe Card opposite from the side to which the substrate is connected.

The following describes another method (“Method IV”) for connecting aflexible substrate (sometimes referred to as a “flex substrate”) to aProbe Card (i.e., for connecting BGA pads of the flex substrate to BGApads of the Probe Card) in accordance with one or more embodiments ofthe present invention. A suitable flex substrate may be fabricated frompolyimide or from any other suitable materials that are well known tothose of ordinary skill in the art. In accordance with one or more suchembodiments, the flex substrate has a thickness in a range from, forexample and without limitation, about 1 mil to about 3 mils to provide apredetermined degree of flexibility. The degree of flexibility that maybe utilized in a particular application may be determined, for exampleand without limitation, readily by one of ordinary skill in the artwithout undue experimentation by testing.

FIG. 2 is a top view that shows a portion of flex substrate 175 that isfabricated in accordance with one or more embodiments of the presentinvention. As shown in FIG. 2, and in accordance with one or more suchembodiments of the present invention, the BGA pads on the bottom ornon-testing side of flex substrate 175 (i.e., the side oppositecontactors 177 ₁-177 ₆) is laid out in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart so that the following is true for a predetermined fraction of theBGA pads for a particular grid, for example and without, a 0.8 mm gridor a 0.65 mm grid. An area surrounded by pads 179 ₁-179 ₄ (shown inphantom in FIG. 2) encompasses contactors 177 ₁-177 ₆. Next, inaccordance with one or more such embodiments of the present invention,the substrate is connected to the Probe Card using interconnectors suchas, for example and without limitation, any of the interconnectorsdescribed above in conjunction with Methods I or II; and the substrateand the Probe Card are connected utilizing any of the embodimentsdescribed above in conjunction with Method I or Method II.Advantageously, in accordance with one or more such embodiments of thepresent invention, during use in a Tester or Test System, the flexsubstrate acts like a drum membrane. As a result, whenever a structurefabricated in accordance with this embodiment of the present inventionis used in a Tester, the contactors are able to move distances that makeup for at least some non-planarity in the structure itself, and/or forany non-uniformity in bump height on the wafer.

The following describes another method (“Method V”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) in accordance with one or more embodimentsof the present invention, which substrate can be, for example andwithout limitation, a rigid substrate, a flex substrate, or a semi-flexsubstrate.

In a first step of Method V, a thickness of at least two edges of asubstrate such as, for example and without limitation, a rigidsubstrate, is reduced by use of any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, using a router, a laser, and so forth to formbevels. FIGS. 3-5 are cross sectional views that show substrates 186,187, and 188, respectively, that have bevels formed on the edges ofthereof in accordance with one or more embodiments of the presentinvention. In accordance with one such embodiment, the thickness of theedge of the substrate is reduced to a thickness in a range, for exampleand without limitation, from about 0.2 mm to about 0.3 mm.

Next, compliant interconnectors such as, for example and withoutlimitation, compliant, conductive balls or springs (such as, for exampleand without limitation, compliant, conductive balls or springs likethose described above in conjunction with Methods I or II) are connectedto the substrate utilizing any of the embodiments described above inconjunction with Part I of Method II.

Next, an optional interconnector alignment film (for example and withoutlimitation, a polyimide film like that described above having holes init that align to the Probe Card pads), may be affixed to the Probe Cardutilizing methods described above in conjunction with, for example,Method I. Such an interconnector alignment film would act as a guide forthe balls or springs.

Next, electrical connection between pads on the substrate and pads onthe Probe Card is provided by a clamp mechanism shown in FIG. 6. Asshown in FIG. 6, the clamp mechanism includes: (a) substrate cover 310;(b) a connection mechanism shown, for example and without limitation, asa releasable connection mechanism comprised of screws 305 ₁-305 ₄ andnuts 307 ₁-307 ₄; and (c) guide pins 320 ₁-320 ₄. As shown in FIG. 6,guide pins 320 ₁-320 ₄ are used to align the substrate to holes 325₁-325 ₄ in Probe Card 330, and to align substrate cover 310 over thesubstrate so that the balls or springs connected to the substrate arealigned with pads on Probe Card 330. As further shown in FIG. 6,substrate cover 310 includes a recess that is formed by lip 327. Asfurther shown in FIG. 6, area 329 of the recess in substrate cover 310is open to enable access to contactors disposed on a top side of thesubstrate during testing. In addition, lip 327 of substrate cover 310 isformed so that it fits over the beveled edges of the substrate to holdthe substrate in place when the structure is assembled. Guide pins 320₁-320 ₄ are removed after substrate cover 310 is connected to Probe Card330 using, for example and without limitation, a connection mechanism,for example and without limitation, a releasable connection mechanismcomprised of screws 305 ₁-305 ₄ and nuts 307 ₁-307 ₄. In accordance withone or more such embodiments, electrical contact is ensured by pressureapplied by the wafer during testing. In addition, a stiffening mechanismlike that described above may be (optionally) connected to a side of theProbe Card opposite from the side to which the substrate is connected.It should be understood that in one or more alternatives of theabove-described embodiment, the substrate may not have bevels formed inthe sides, and lip 327 of substrate cover 310 is formed so that it fitsover the edges of the substrate to hold the substrate in place when thestructure is assembled.

In accordance with one or more further alternatives of theabove-described embodiment, instead of connecting the conductive,compliant balls or springs to the substrate (as described above), theyare connected to Probe Card 330 using the same steps set forth above forconnecting the conductive, compliant balls or springs to the substrate.In accordance with such further alternative embodiments, a polyimidefilm may be applied to the Probe Card to support the balls or springs aswas done in Method I, however, this is not necessary. Next, electricalconnection between pads on the substrate and pads on the Probe Card isprovided by using the clamp mechanism shown in FIG. 6. In either case,if the substrate wears out or is damaged, it is easily replaced byreleasing the connection mechanism, for example and without limitation,by removing screws 305 ₁-305 ₄, thereby causing minimum equipmentdowntime. Advantageously, compliant balls or springs may make up for atleast some non-planarity in the structure itself, and/or for anynon-uniformity in bump height on the wafer.

The following describes another method (“Method VI”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) in accordance with one or more embodimentsof the present invention. In accordance with one or more embodiments ofthe present invention, the substrate is a chip having spring-typecontactors on a testing side, which chip is fabricated, for example andwithout limitation, using standard MEMS technology. In accordance withone or more such embodiments, each contactor is wired through vias onthe chip to make contact with pads on the bottom side of the chip inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art. Advantageously, the spring typecontactors on the top of the chip make up for at least somenon-planarity in the structure itself, and/or for any non-uniformity inbump height on the wafer. The chip may be connected to the Probe Cardusing any one of the above-described embodiments. For example, FIG. 7 isa cross sectional view that shows chip substrate 360 that is fabricatedin accordance with one or more embodiments of the present invention. Asshown in FIG. 7, chip substrate 360 includes bevels 361 ₁-361 ₂;alignment vias 367 ₁-367 ₂; spring-type contactors 363 ₁-363 ₂; wiring369 ₁-369 ₂; and pads 367 ₁-367 ₂ to enable use of one or moreembodiments of Method V above.

The following describes another method (“Method VII”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) to provide an inventive structure inaccordance with one or more embodiments of the present invention. Inaccordance with one or more such embodiments, the inventive structurecomprises a substrate, a Probe Card, and an interconnector in the formof a connector-holder that is aligned to the substrate and the ProbeCard, wherein electrical connections between pads on the substrate andpads on the Probe Cards are made through the connector-holder utilizingelectrical connectors such as, for example and without limitation,electrical connectors having first and second retractable ends (forexample, Pogo pins). Advantageously, in accordance with one or more suchembodiments of the present invention, inventive structures are producedthat may be used cost effectively for testing because, among otherreasons, the substrate may be replaced easily and rapidly with a new onewhen the substrate is damaged or worn.

In accordance with one or more embodiments of the present invention, aflexible, HDI substrate is fabricated utilizing, for example and withoutlimitation, polyimide, Teflon, and so forth in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art. In accordance with one or more such embodiments of the presentinvention, the substrate has a thickness in a range, for example andwithout limitation, from about 2 mils to about 3 mils, and the substratehas contactors disposed on a top side of the substrate in an array thathas the same pitch as that of bumps on a chip on a wafer to be tested.The contactors are wired through vias in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart, and the wires contact BGA pads disposed on a bottom side of thesubstrate, which BGA pads are disposed in a grid array that has apredetermined grid array spacing, for example and without limitation, aspacing in a range from about 0.65 mm to about 1.27 mm. Although it isnot required to utilize a flex substrate to carry out Method VII, oneadvantage of using a flex substrate is that the resulting structure maymake up for at least some non-planarity in the structure itself, and/orfor any non-uniformity in bump height on the wafer. This is becausemovement in a Z-axis (i.e., an axis perpendicular to a plane of thesubstrate) is provided by the flex substrate, with or without the needfor compliant connectors disposed between it and the Probe Card.

In accordance with Part I of Method VII, a connector-holder isfabricated. In accordance with one or more such embodiments, theconnectors are electrical connectors having first and second retractableends (for example, Pogo pins), and the connector-holder for these Pogopins is fabricated from plastic such as, for example and withoutlimitation, ULTEM™, Torlon, and so forth. FIG. 8 shows Pogo pin 800 thatis commercially available from any one of a number of sources. As shownin FIG. 8, Pogo pin 800 includes plungers 810 and 811 and barrel 820.Pogo pin 800 provides an electrical conduit between the tips of plungers810 and 811, and as such, it is preferable that the tips of plungers 810and 811 of Pogo pin 800 be narrow to enable better electrical contactwith the pads. As such, plungers 810 and 811 may be fabricated, forexample and without limitation, of gold-plated hardened steel; barrel820 may be fabricated, for example and without limitation, of agold-plated copper alloy; and internal springs (not shown) may befabricated, for example and without limitation, of gold-plated pianowire.

The connector-holder comprises a connector-holder bottom plate and aconnector-holder top plate that are both fabricated, for example andwithout limitation, from plastic. FIG. 9 is a top perspective view thatshows connector-holder bottom plate 600 that is fabricated in accordancewith one embodiment of the present invention, and FIG. 10 is a bottomperspective view that shows connector-holder top plate 700 that isfabricated in accordance with one embodiment of the present invention.Connector-holder bottom plate 600 and connector-holder top plate 700 maybe fabricated in accordance with any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, by injection molding, and holes may befabricated therein in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art such as, forexample and without limitation, by drilling. Referring to FIG. 9, thelocations of the holes in array 610 of connector-holder bottom plate 600match the locations of BGA pads on the Probe Card. Further, referring toFIG. 10, the locations of the holes in array 710 of connector-holder topplate 700 match the locations of BGA pads on the substrate. Stillfurther, in accordance with one or more embodiments of the presentinvention, the holes in array 610 of connector-holder bottom plate 600(such as hole 615 shown in FIG. 11) comprise hole 616 within hole 617for retaining Pogo pins in place when connector-holder bottom plate 600and connector-holder top plate 700 are connected. For example, (a) thediameter of hole 616 is larger—preferably by a small amount—(for exampleand without limitation, the diameter of hole 616 is in a range fromabout 1 mil to about 3 mils) than the diameter of plunger 810 of Pogopin 800 shown in FIG. 8; and (b) the diameter of hole 617larger—preferably by a small amount—than the diameter of barrel 820 ofPogo pin 800. Yet still further, in accordance with one or moreembodiments of the present invention, the holes in array 710 ofconnector-holder top plate 700 (such as hole 715 shown in FIG. 12)comprise hole 716 within hole 717 for retaining Pogo pins in place whenconnector-holder bottom plate 600 and connector-holder top plate 700 areconnected. For example, the (a) the diameter of hole 716 islarger—preferably by a small amount—than the diameter of plunger 811 ofPogo pin 800; and (b) the diameter of hole 717 is larger—preferably by asmall amount—than the diameter of barrel 820 of Pogo pin 800.

As shown in FIG. 9, connector-holder bottom plate 600 includes posts 611₁-611 ₄. Posts 611 ₁-611 ₄ include holes for connection mechanisms (forexample and without limitation, releasable connection mechanisms)comprised, for example and without limitation, of screws 937 ₁-937 ₄(shown in FIG. 13) that are used to hold connector-holder bottom plate600 and connector-holder top plate 700 together (as will be describedbelow). As further shown in FIG. 10, connector-holder top plate 700includes receptacles 711 ₁-711 ₄. Receptacles 711 ₁-711 ₄ include holesfor the connection mechanisms (for example and without limitation,releasable connection mechanisms) comprised, for example and withoutlimitation, of screws 937 ₁-937 ₄ (shown in FIG. 13) that are used tohold connector-holder bottom plate 600 and connector-holder top plate700 together (as will be described below). The shape of receptacles 711₁-711 ₄ is such that posts 611 ₁-611 ₄, mate with receptacles 711 ₁-711₄ when connector-holder bottom plate 600 and connector-holder top plate700 are connected to each other. As still further shown in FIG. 10,connector-holder top plate 700 further includes: (a) vias 712 ₁-712 ₄that are used for guide pins 910 ₁-910 ₄ (shown in FIG. 13); and (b)holes 713 ₁-713 ₄ that are used for connection mechanisms (for exampleand without limitation, releasable connection mechanisms) comprised, forexample and without limitation, of screws 940 ₁-940 ₄ (shown in FIG. 13)to hold the connector-holder in place after final assembly (as will bedescribed below).

To assemble the connector-holder in accordance with one or moreembodiments of the present invention: (a) Pogo pins are placed into theholes of array 710 of connector-holder top plate 700; (b)connector-holder bottom plate 600 is then placed over connector-holdertop plate 700; and (c) as indicated in FIG. 13, connector-holder bottomplate 600 is connected to connector-holder top plate 700 by screwingconnector-holder bottom plate 600 into connector-holder top plate 700 atfour (4) corners using screws 937 ₁-937 ₄.

In accordance with Method VII, vias are formed for guide pins 910 ₁-910₄ (shown in FIG. 13) in the substrate and the Probe Card in accordancewith any one of a number of methods that are well known to those ofordinary skill in the art.

FIG. 13 is an exploded view that shows a portion of a structure used totest circuits that is fabricated in accordance with one or moreembodiments of the present invention. Clamp 930 (a bottom perspectiveview of clamp 930 is shown in FIG. 13) includes: (a) vias 965 ₁-965 ₄that are used for guide pins 910 ₁-910 ₄ (shown in FIG. 13); and (b)holes 961 ₁-961 ₄ that are used for screws 940 ₁-940 ₄ (shown in FIG.13) to hold the connector-holder and the substrate in place on ProbeCard 920 (as will be described below). As shown in FIG. 13, clamp 930includes a recess that is formed by lip 978. As further shown in FIG.13, area 987 of the recess in clamp 930 is open to enable access tocontactors disposed on a top side of the substrate during testing. Inaddition, lip 978 is formed so that it fits over, and may make contactwith the edges or any bevels in the edges, of the substrate when thestructure is assembled. Clamp 930 is fabricated, for example and withoutlimitation, from plastic in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by injection molding, and holesmay be fabricated therein in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by drilling.

In accordance with one embodiment of Part II of Method VII, thesubstrate is connected to the connector-holder fabricated in accordancewith Part I of Method VII. In a first optional step of this embodimentof Part II of Method VII, a thickness of at least two edges of asubstrate is reduced by use of any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, using a router, a laser, and so forth to formbevels like those fabricated in accordance with Method V. The thicknessof the routed edges is a function of the Z-movement of the Pogo pinsused to fabricate the connector-holder described above.

Next, in another optional step of this embodiment of Part II of MethodVII, a release film such as, for example and without limitation, arelease film like that described above in conjunction with Method I) isaligned with, and placed over, a base plate of a pinalignment fixture(such as, for example and without limitation, a base plate and apinalignment fixture like those described above in conjunction withMethod I). Next, a substrate is aligned with, and placed over, therelease film on the pinalignment fixture with its BGA pads side up.Next, a paste stencil mask that is fabricated in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art is aligned with, and placed over, the substrate on thepinalignment fixture. Next, a paste such as, for example and withoutlimitation, a no-clean solder paste is applied onto the BGA pads of thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art such as, for example and withoutlimitation, methods utilizing a dispensing machine, methods utilizingscreen-printing, methods utilizing a squeegee, and so forth. Also, inaccordance with one or more further embodiments of the presentinvention, the paste may be any one of a number of conductive pastesthat are well known to those of ordinary skill in the art such as, forexample, and without limitation, a Ag conductive paste, a Au conductivepaste, a Cu conductive paste, and so forth, or it may be any one of anumber of solder pastes that are well known to those of ordinary skillin the art. Further, the paste can be a compliant, conductive pastewhere such compliant conductive paste may be any one of a number of suchproducts that are well known to those of ordinary skill in the art suchas, for example and without limitation, an elastomer such as a siliconeelastomer having conductive particles embedded therein. Next, the pastestencil mask is removed.

Next, in accordance with this embodiment of Part II of Method VII, aconnector-holder fabricated in accordance with Part I of Method VII ispinaligned (using two or more of guide pins 910 ₁-910 ₄ shown in FIG.13) to the substrate fabricated in accordance with Part II of MethodVII. Next, the resulting substrate structure is re-flowed or cured,depending on the type of paste used, to connect the Pogo pins to the BGApads on the substrate.

Next, two or more of guide or dowel pins 910 ₁-910 ₄ are used to alignthe resulting substrate structure with, and place the resultingsubstrate structure over, Probe Card 920 so that the tips of the Pogopins align with the pads on Probe Card 920. Finally, clamp 930 isaligned with, and placed over, Probe Card 920 utilizing two or more ofguide or dowel pins 910 ₁-910 ₄, and clamp 930 is connected to ProbeCard 920 utilizing screws 940 ₁-940 ₄ (screws 940 ₁-940 ₄ also passthrough the connector-holder) and nuts 950 ₁-950 ₄, thereby holding thefinal assembly in place. Alternatively, clamp 930 and theconnector-holder may be connected to Probe Card separately. Next, theguide pins are removed. In addition, a stiffening mechanism like thatdescribed above may be (optionally) connected to a side of the ProbeCard opposite from the side to which the substrate is connected.

Advantageously, using a flex substrate and Pogo pins in accordance withthe above-described embodiments enables bump height non-uniformity ornon-planarity of the structure to be made up by movement in a Z-axisduring testing. Further, a short interconnection distance between thesubstrate and the Probe Card obtained from the use of small Pogo pinscan create better electrical properties than those of structuresproduced using prior art methods. Still further, in accordance with theabove-described embodiments, whenever the flex substrate wears out orbecomes damaged, the Pogo pins can be removed from it by de-soldering inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art. Then a new substrate may beincorporated into the assembly, and the Probe Card may be reused.

In accordance with one or more alternative embodiments of Method VIIdescribed above, the substrate is laid out in accordance with any one ofa number of methods that are well known to those of ordinary skill inthe art so that all the wiring to the bottom side of the substrate(i.e., the side opposite from the contactors) is routed to a peripheryof the substrate. As a result, in accordance with this embodiment of thepresent invention, there are no pads underneath contactors disposed in aregion of the substrate, for example and without limitation, a center ofthe substrate. Next, a compliant substance such as, for example andwithout limitation, a compliant elastomer, is applied to the bottom sideof the substrate, in the central area, in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart such as, for example and without limitation, by screen printing orstenciling methods. The compliant substance would be thick enough sothat it contacts connector-holder top plate 700 when the substrate isconnected to the connector-holder as described above. Since the pads onthe bottom side of the substrate are on the periphery of the substrate,so too are the Pogo pins held by the connector-holder disposed about theperiphery of the substrate. As a result, whenever the contactors on thesubstrate move up and down during testing, the substrate can flexsufficiently to make up for at least some non-planarity in the structureitself, and/or for any non-uniformity in bump height on the wafer. Inaddition, in accordance with one or more further such alternativeembodiments, the connector-holder has a hole in the middle, and thecompliant substance applied to the bottom side of the substrate is madeso thick that it extends through to the Probe Card, which Probe Card mayalso be milled to provide a recessed area into which the substance isseated.

The following describes another method (“Method VIII”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) in accordance with one or more embodimentsof the present invention, which substrate can be, for example andwithout limitation, a rigid substrate, a semi-rigid substrate, asilicon/glass substrate having MEMS-type springs, and so forth.

In accordance with Part I of Method VIII, an interconnector in the formof a connector-holder is fabricated in accordance with Part I of MethodVII. Next, vias are formed for guide pins in the substrate and the ProbeCard in accordance with any one of a number of methods that are wellknown to those of ordinary skill in the art.

Next, clamp 960 is fabricated, for example and without limitation, fromplastic in accordance with any one of a number of methods that are wellknown to those of ordinary skill in the art such as, for example andwithout limitation, by injection molding. Holes may be fabricated inclamp 960 in accordance with any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, by drilling. FIG. 15 is a top view that showsclamp 960. As shown in FIG. 15, clamp 960 includes: (a) vias 975 ₁-975 ₄that are used for to guide pins (to be described below); and (b) holes971 ₁-971 ₄ that are used for connection mechanisms, for example andwithout limitation, releasable connection mechanisms comprised ofscrews, (to be described below) to connect clamp 960 to theconnector-holder. As further shown in FIG. 15, clamp 960 includesstationary structures 981 ₁ and 981 ₂ which have lips (shown in phantom)that are disposed to cover a portion of the edges or any bevels in theedges (see below) of the substrate and to engage (optional) grooves inthe beveled edges of the substrate. As further shown in FIG. 15, clamp960 includes a substrate alignment mechanism. In particular, as furthershown in FIG. 15, clamp 960 includes laterally movable structures 981 ₃and 981 ₄ which have lips (shown in phantom) that are disposed to coverat least a portion of the beveled edges (see below) of the substrate andto engage (optional) grooves in the beveled edges of the substrate. Asfurther shown in FIG. 15, clamp 960 includes springs 991 ₁ and 991 ₂ andsprings 991 ₃ and 991 ₄. Springs 991 ₁ and 991 ₂ urge movable structure981 ₃ toward the center of clamp 960, and springs 991 ₃ and 991 ₄ urgemovable structure 981 ₄ toward the center of clamp 960. In use, whenclamp 960 is placed over the substrate (see below), stationarystructures 981 ₁ and 981 ₂ and movable structures 981 ₃ and 981 ₄ engagethe edges of the substrate (for example and without limitation, ingrooves disposed therein), and springs 991 ₁, 991 ₂, 991 ₃, and 991 ₄provide lateral forces that help align the substrate. Those of ordinaryskill in the art should understand that (although the embodimentdescribed above in conjunction with FIG. 15 indicated that structures981 ₁ and 981 ₂ were stationary and that structures 981 ₃ and 981 ₄ werelaterally movable) further embodiments exist where all of some ofstructures 981 ₁-981 ₄ are movable. For example and without limitation,in accordance with one or more further embodiments, structures 981 ₁ and981 ₄ are movable and structures 981 ₂ and 981 ₃ are stationary, or viceversa.

In accordance with Part II of Method VIII, first, (optionally) athickness of at least two edges of the substrate is reduced by use ofany one of a number of methods that are well known to those of ordinaryskill in the art such as, for example and without limitation, using arouter, a laser, and so forth to form bevels like those fabricated inaccordance with Method V. The thickness of the routed edges is afunction of the Z-movement of the Pogo pins used to fabricate theconnector-holder. Next, optional grooves, for example and withoutlimitation, V-shape grooves are cut into two or more sides of thesubstrate in accordance with any one of a number of methods that arewell known to those of ordinary skill in the art. FIG. 14 is a crosssectional view that shows an edge of the substrate with groove 657.

Next, guide or dowel pins are used to align the connector-holder withthe Probe Card (as a result, Pogo pins in the connector-holder areconnected to pads on the Probe Card). Once the connector-holder isaligned with respect to the Probe Card, the connector-holder isconnected to the Probe Card using a connection mechanism, for exampleand without limitation, a releasable connection mechanism comprised ofscrews and nuts. For example, four (4) screws are inserted through theconnector-holder and the Probe Card, and four (4) nuts are secured tothe screws to connect the connector-holder and the Probe Card. Next, theguide or dowel pins are removed. Next, the substrate is aligned with,and placed over, the connector-holder (two or more guide or dowel pinsare used to align the Pogo pins of the connector-holder with the BGApads of the substrate). Next, clamp 960 is aligned with, and placedover, the substrate (two or more guide or dowel pins are use to alignthe clamp and the substrate), and clamp 960 is connected to theconnector-holder using a connection mechanism, for example and withoutlimitation, a releasable connection mechanism comprised of screws. Forexample, four (4) screws are screwed into the connector-holder. Asdescribed above, clamp 960 confines vertical movement of the substrateas well as providing lateral alignment by spring action. In addition, astiffening mechanism like that described above may be (optionally)connected to a side of the Probe Card opposite from the side to whichthe substrate is connected. The Probe Card/substrate assembly is nowready for use in testing circuits.

In accordance with one or more further such embodiments of the presentinvention, a connector-holder is not fixedly connected to the ProbeCard, and a clamp is connected directly to the Probe Card, which clampwould include a connector-holder alignment mechanism and a substratealignment mechanism. For example and without limitation, in accordancewith such further embodiments, the connector-holder alignment mechanismand the substrate alignment mechanism may be fabricated utilizingmovable structures and springs like those described above in conjunctionwith clamp 960.

In accordance with one or more such embodiments, advantageously,whenever the substrate wears out or becomes damaged, it is replacedwhile the Pogo pins stay in place and get reused. If a Pogo pin isdamaged, it can easily be pulled out of the connector-holder and bereplaced. Advantageously, since neither the connector-holder nor thePogo pins get replaced (unless a Pogo pin is damaged), there is minimumdowntime required for replacing the substrate. In addition, a shortinterconnection distance between the substrate and the Probe Cardobtained from the use of small Pogo pins can create better electricalproperties than those of structures produced using prior art methods.

Note that if one substrate is not sufficient to handle the wiringdensity required for a circuit or IC having lots of I/O (for example andwithout limitation, a circuit having >3000 I/O connections), a compositesubstrate may be fabricated which comprises a first level substrate anda second level substrate that is connected to the first level substrate.Electrical connection between the first level substrate and the secondlevel substrate can be made using any of the methods described aboveutilizing interconnectors such as, for example and without limitation,any of the interconnectors described above in conjunction with Methods Ior II; and the two substrates are connected utilizing any of theembodiments described above in conjunction with, for example and withoutlimitation, Method I or Method II. The composite substrate may then beconnected to the Probe Card utilizing any of the methods describedabove.

One or more further embodiments of the present invention relate to aProbe Card that can function as a universal Probe Card, i.e., a ProbeCard that may be useful in a number of different testing applications.In accordance with such one or more further embodiments, the Probe Cardhas a large number of pads disposed in a grid having, for example andwithout limitation, at least about four hundred (400) pads and having,for example and without limitation, a 0.8 mm pad pitch. As is wellknown, for a typical Probe Card, connections to analog I/O on a chip aregrouped and connected to one cluster of pins on the outside of the ProbeCard, and connections to digital I/O on the chip are grouped andconnected to another cluster of pins on the outside of the Probe Card.Thus, in accordance with one such further embodiment of the presentinvention, the above described universal Probe Card would allocate a onefraction of its pads to analog I/O and another fraction of its pads todigital I/O. The allocation would be such that there would be asufficient number of connections to analog I/O and to digital I/O tosatisfy the required number of connections for a number of differentchip designs. This would enable the Probe Card to be used in a number ofdifferent testing applications. Then, in accordance with one suchfurther embodiment of the present invention, a substrate specific to theparticular chip being tested would be used with the universal ProbeCard. Advantageously, the various specific substrates useful for thevarious specific applications would be connected to the universal ProbeCard utilizing one or more of the methods described herein.

One or more further embodiments of the present invention relate to astructure for testing circuits that is fabricated in accordance with oneor more embodiments of the present invention. FIG. 16 is a crosssectional view that shows structure 2001 that is fabricated inaccordance with one or more embodiments of the present invention. Asshown in FIG. 16, structure 2001 comprises substrate 2000, RF interfaceboard 2100, and Probe Card 2200. As further shown in FIG. 16, substrate2000 includes array 2010 of contactors on a top or testing side thereof(i.e., a side that contacts an IC on the wafer). As further shown inFIG. 16, RF interface board 2100 is connected, on a top side thereof, toBGA pads disposed on a bottom side of substrate 2000 by means of, forexample and without limitation, conductive balls 2020. As further shownin FIG. 16, RF interface board 2100 is further connected so that: (a)non-RF I/O BGA pads on a bottom side of RF interface board 2100 areconnected to BGA pads on a top side of Probe Card 2200 by means of, forexample and without limitation, conductive balls 2030, and (b) RFcoaxial cable connectors (not shown) on a bottom side of RF interfaceboard 2100 are connected to RF test coaxial cables 2110. As furthershown in FIG. 16, RF test coaxial cables 2110 are routed throughchannels 2220 in Probe Card 2200.

FIG. 17 is a top view that shows substrate 2000 and RF interface board2100 of structure 2001. As shown in FIG. 17, RF interface board 2100includes wing structures 2110 ₁-2110 ₄ (i.e., extension structureshaving perimeters wherein at least a portion of these perimeters extendbeyond a perimeter of substrate 2000). As further shown in FIG. 17, wingstructures 2110 ₁-2110 ₄ include wiring groups 2120 ₁-2120 ₄ (shown inphantom), respectively. In accordance with one or more embodiments ofthe present invention, wiring groups 2120 ₁-2120 ₄ provide electricalconnections from RF I/O BGA pads on a top side of RF interface board2100 to RF coaxial cable connectors (not shown) on a bottom side of RFinterface board 2100. In addition, RF interface board 2100 includeswiring (not shown) that provides electrical connections from non-RF I/OBGA pads on the top side of RF interface board 2100 to non-RF I/O BGApads on the bottom side of RF interface board 2100. RF interface board2100 may be fabricated in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art usingmaterials utilized to fabricate a rigid substrate, a semi-flexsubstrate, a flex substrate, a silicon/glass structure, and so forth,and using any one of a number of RF coaxial cable connectors that arewell known to those of ordinary skill in the art. Note that although RFinterface board 2100 described above includes wing structures 2110₁-2110 ₄ shown in FIG. 17, further embodiments of the present inventionexist in which structures used to connect to RF I/O may take any one ofa number of forms such as, for example and without limitation, a singleboard whose periphery carries RF connectors, one or more wings, and soforth.

In use for testing, structure 2001 might be connected to, for exampleand without limitation, a Pogo Tower (a Pogo Tower is a type ofconnector that is well known to those of ordinary skill in the art andwhich is used in some commercial test systems to provide an interface toa Probe Card). For example, in such an arrangement, a top side of thePogo Tower would be connected to non-RF test connectors 2210 (shown inFIG. 16) on a bottom side of Probe Card 2200 in a well known manner, anda bottom side of the Pogo Tower would be connected to a test systeminterface board in a well known manner. Further, RF test coaxial cables2110 (which are routed through channels 2220 in Probe Card 2200) wouldbe further routed through a central aperture in the Pogo Tower (manycommercial embodiments of a Pogo Tower are fabricated to have anaperture in the center), and would be connected directly to the testsystem interface.

In accordance with one or more such embodiments of the presentinvention, substrate 2000 may be any of the substrates that have beendescribed herein such as, for example and without limitation, a rigidsubstrate, a flex substrate, a semi-flex substrate, a silicon/glasssubstrate (for example and without limitation, a silicon/glass structurethat includes MEMS-type spring contactors), and so forth. In addition,Probe Card 2200 may be any one of a number of Probe Cards that are wellknown to those of ordinary skill in the art. Channels 2220 in Probe Card2200 may be fabricated in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art such as, forexample and without limitation, by drilling. Further, channels 2220 aremade large enough to enable the desired number of coaxial cables to fitthrough.

In fabricating structure 2001 described above, one may utilize any ofthe above-described methods to connect substrate 2000 to RF interfaceboard 2100, and to connect RF interface board 2100 to Probe Card 2200.Thus, as one can readily appreciate from the above, and in accordancewith one or more such embodiments of the present invention, the coaxialcables are connected close to contactors 2010, and the Pogo Tower isbypassed, thereby decreasing an electrical path between contactors onthe substrate and the Test System. As a result, it is expected thatbetter electrical performance will be achieved when using the inventivestructures when compared to that of structures fabricated in accordancewith the prior art.

One or more further embodiments of the present invention relate to astructure for testing circuits that is fabricated in accordance with oneor more embodiments of the present invention. FIG. 18 is a crosssectional view of structure 3000 that is fabricated in accordance withone or more embodiments of the present invention. As shown in FIG. 18,structure 3000 includes flex substrate 3010. Flex substrate 3010 isfabricated from any one of a number of flexible materials that are wellknown to those of ordinary skill in the art such as, for example andwithout limitation, polyimide, liquid crystal polymer (“LCP”), Teflon,and so forth. In addition, flex substrate 3010 has circuitry on bothsides, or is a multi-layer structure (for example and withoutlimitation, to provide a multi-level fan-out) depending on the amount ofI/O circuitry on a chip to be tested, which multilayer structure may befabricated in accordance with one or more of the methods describedherein. As shown in FIG. 18, flexible substrate 3010 has an array ofcontactors (for example, posts or bumps 3005 ₁-3005 ₂) located on a topor testing side (i.e., a side that contacts an IC on a wafer), whichcontactors make contact with bumped or non-bumped pads of a IC chip on awafer during testing. Posts or bumps on the top side of flex substrate3010 (for example, posts or bumps 3005 ₁-3005 ₂) are connected withtraces through flex substrate 3010 to pads (for example, pads 3015₁-3015 ₂) on the bottom side of flex substrate 3010. In accordance withone or more embodiments of the present invention, pads 3015 ₁-3015 ₂ areon the periphery of the array of contactors on the top side of flexsubstrate 3010, i.e., pads 3015 ₁-3015 ₂ are not under posts or bumps3005 ₁-3005 ₂. Posts or bumps 3005 ₁-3005 ₂ may have a height, forexample and without limitation, in a range from about 40 μm to about 60μm. Further, the posts or bumps on the top side of flex substrate 3010,the traces, and the pads on the bottom side of flex substrate 3010 maybe fabricated using any one of a number of methods that are well knownto those of ordinary skill in the art. For example and withoutlimitation, the pads (for example, pads 3015 ₁-3015 ₂) on the bottomside of flex substrate 3010 may be fabricated from alloys such asCu/Ni/Au, Ni/Au and so forth.

As further shown in FIG. 18, substrate 3020 is a rigid substrate. Inaccordance with one or more embodiments of the present invention,substrate 3020 has no circuitry. Substrate 3020 may be fabricated, forexample and without limitation, from FR-4 glass epoxy substrates, BTepoxy materials, and so forth, and may have a thickness in a range, forexample and without limitation, from about 0.5 mm to about 1.5 mm. Inaccordance with one or more embodiments of the present invention, thearea of substrate 3020 (in a plane perpendicular to the plane of FIG.18) is larger than the area of flex substrate 3010 (also in a planeperpendicular to the plane of FIG. 18). As further shown in FIG. 18,substrate 3020 includes vias (for example, vias 3027 ₁-3027 ₂) in anarray whose locations are aligned with the locations of the pads (forexample, pads 3015 ₁-3015 ₂) on the bottom side of flex substrate 3010.The vias (for example, vias 3027 ₁-3027 ₂) surround at least a portionof a barrel of electrical connectors having first and second retractableends such as, for example and without limitation, Pogo pins (forexample, Pogo pins 3030 ₁-3030 ₂), wherein the diameter of the vias is afunction of the diameter of the barrel of the Pogo pins. The Pogo pinsshown in FIG. 18 (for example, Pogo pins 3030 ₁-3030 ₂) are like Pogopin 800 described above. As further shown in FIG. 18, the vias (forexample, vias 3027 ₁-3027 ₂) are disposed so that retractable ends ofthe Pogo pins (for example, Pogo pins 3030 ₁-3030 ₂) contact pads (forexample, pads 3015 ₁-3015 ₂) on the bottom side of flex substrate 3010when structure 3000 is assembled in the manner described herein.

As further shown in FIG. 18, compliant adhesive layer 3040 includes viasthat are aligned with the pads (for example, pads 3015 ₁-3015 ₂) on thebottom side of flex substrate 3010. Compliant adhesive layer 3040 may befabricated using any one of a number of materials that are well known tothose of ordinary skill in the art such as, for example and withoutlimitation, a silicon elastomer, a flexible epoxy, and so forth.

A pinalignment fixture like that described above may be used in a firststage of a method for assembling structure 3000. In a first, optionalstep, a release film such as, for example and without limitation, aMylar film or a Teflon film, is aligned with, and placed over, a baseplate of the pinalignment fixture (as was described above, holes in therelease film match the positions of alignment pins). Next, flexsubstrate 3010 is aligned with, and placed over, the release film on thepinalignment fixture (holes in flex substrate 3010 (not shown) match thepositions of the alignment pins). Next, compliant adhesive layer 3040 isaligned with, and placed over flex substrate 3010 on the pin alignmentstructure (holes in compliant adhesive layer 3040 (not shown) match thepositions of the alignment pins). Next, rigid substrate 3020 is alignedwith, and placed over compliant adhesive layer 3040 (holes in rigidsubstrate 3020 (not shown) match the positions of the alignment pins).Next, a weight, for example, an aluminum or stainless steel plate havinga thickness in a range, for example and without limitation, from about10 mm to about 12.7 mm, and having an area of about the same size asthat of compliant adhesive layer 3040, is aligned with, and placed overrigid substrate 3020 to apply pressure to compliant adhesive layer 3040(holes in the weight match the positions of the alignment pins). Next,flex substrate 3010 may be laminated to rigid substrate 3020 by, forexample and without limitation, baking in an oven. The oven temperaturemay be in a range, for example and without limitation, from about 150°C. to about 200° C., the pressure exerted by the weight may be in arange, for example and without limitation, from about 14 kg/cm² to about28 kg/cm², and the time spent in the oven may be in a range, for exampleand without limitation, from about 1 hour to about 2 hours. Next, theintermediary structure is removed from the pinalignment structure.

As further shown in FIG. 18, socket interposer 3050 is formed, forexample and without limitation, from plastic such as ULTEM™, Torlon, andso forth. Socket interposer 3050 includes holes (for example, holes 3045₁-3045 ₂) in an array whose locations are aligned with the locations ofthe pads (for example, pads 3015 ₁-3015 ₂) on the bottom side of flexsubstrate 3010. As further shown in FIG. 18, each of the holes in socketinterposer 3050 (for example, holes 3045 ₁-3045 ₂) comprises a holewithin a hole for seating the Pogo pins (for example, Pogo pins 3030₁-3030 ₂) when structure 3000 is assembled in the manner describedherein (also refer to the discussion of connector-holder bottom plate600 above in conjunction with FIG. 11 to understand the manner in whichsuch holes retain Pogo pins). Note that one or more alternativeembodiments may not utilize the hole within a hole seating mechanism.

As further shown in FIG. 18, socket interposer 3050 also includes: (a)threaded holes (for example, holes 3047 ₁-3047 ₂) that locate connectionmechanisms (for example and without limitation, releasable connectionmechanisms) comprised, for example and without limitation, of screws3052 ₁-3052 ₂, which connection mechanisms are used to connect socketinterposer 3050 and clamp 3060 (as will be described below); and (b)holes (for example, holes 3049 ₁-3049 ₂) that locate connectionmechanisms (for example and without limitation, releasable connectionmechanisms) comprised, for example and without limitation, of screws3055 ₁-3055 ₂ and nuts 3057 ₁-3057 ₂, which connection mechanisms areused to connect Probe Card 3070 and socket interposer 3050 (as will bedescribed below). The thickness of socket interposer 3050 is a functionof the length of the Pogo pins. Socket interposer 3050 may be fabricatedin accordance with any one of a number of methods that are well known tothose of ordinary skill in the art such as, for example and withoutlimitation, by injection molding, and the holes may be fabricatedtherein in accordance with any one of a number of methods that are wellknown to those of ordinary skill in the art such as, for example andwithout limitation, by drilling.

As further shown in FIG. 18, clamp 3060 includes: (a) for example andwithout limitation, four (4) holes (for example, holes 3061 ₁-3061 ₂)that locate connection mechanisms (for example and without limitation,releasable connection mechanisms) comprised, for example and withoutlimitation, of screws 3052 ₁-3052 ₂, which connection mechanisms areused to connect socket interposer 3050 and clamp 3060; (b) open region3080 having an area (in a plane perpendicular to the plane of FIG. 18)that is larger than that of flex substrate 3010 and compliant adhesivelayer 3040; (c) lip 3069 that fits over, and makes contact, whenstructure 3000 is assembled, with at least a portion of (and preferablymost of) a portion of substrate 3020 that extends beyond compliantadhesive layer 3040 (for example and without limitation, at least two ormore edges); and (d) wing 3073 that provides a location wherein clamp3060 may be connected to socket interposer 3050.

In a second stage of the method for assembling structure 3000, in afirst optional step, a release film such as, for example and withoutlimitation, a Mylar film or a Teflon film, is aligned with, and placedover, a base plate of the pinalignment fixture (as was described above,holes in the release film match the positions of alignment pins). Next,Probe Card 3070 is aligned with, and placed over, the release film onthe pinalignment fixture (holes in Probe Card 3070 (not shown) match thepositions of the alignment pins). Next, socket interposer 3050 isaligned with, and placed over, Probe Card 3070 on the pinalignmentfixture (holes in socket interposer 3050 (not shown) match the positionsof the alignment pins). Alignment pins are used on opposite corners andplaced through socket interposer 3050 and Probe Card 3070 to align theholes in socket interposer 3050 to the pads on Probe Card 3050. Next,socket interposer 3050 is connected to Probe Card 3070 using connectionmechanisms, for example, by inserting screws (for example, 30551-30552)through socket interposer 3050 and by affixing nuts (for example, nuts30571-30572) to the screws. The alignment pins are then removed. Next,Pogo pins (for example, Pogo pins 30301-30302) are placed inside theholes (for example, holes 30451-30452) in socket interposer 3050. Next,the intermediary structure formed during the first stage is alignedwith, and placed over, socket interposer 3050 on the pinalignmentfixture (holes in substrate 3020 of the intermediary structure (notshown) match the positions of the alignment pins). Next, clamp 3060 isaligned with, and placed over, substrate 3020 and socket interposer 3050on the pinaligmnent fixture (holes in clamp 3060 (not shown) match thepositions of the alignment pins). Next, clamp 3060 is attached to socketinterposer 3050 using connection mechanisms (for example, screws30521-30522) to form structure 3000. The alignment pins going throughsubstrate 3010 and socket interposer 3050 are then removed. At thispoint, structure 3000 is removed from the pinalignment structure.

In accordance with one or more alternative embodiments of the presentinvention, compliant adhesive layer 3040 of structure 3000 is replacedwith a layer wherein an area directly under the post and bumps (forexample, posts or bumps 30051-30052) on the top side of flex substrate3010 is a compliant adhesive material that may be fabricated using anyone of a number of materials that are well known to those of ordinaryskill in the art such as, for example and without limitation, a siliconelastomer, a flexible epoxy, and so forth. Then, in accordance with oneor more such alternative embodiments of the present invention, theremainder of the layer may be a non-compliant adhesive such as, forexample and without limitation, polyimide having an adhesive (forexample and without limitation, epoxy, acrylic, epoxy-acrylic, and soforth) on both sides, and so forth. In accordance with one or morefurther alternative embodiment of the present invention, compliantadhesive layer 3040 of structure 3000 is replaced with a layer whereinan area directly under the post and bumps (for example, posts or bumps30051-30052) on the top side of flex substrate 3010 is open (i.e., airor even some other gas). Then, in accordance with one or more suchfurther alternative embodiments of the present invention, the remainderof the layer may be any of the compliant adhesives described above orany of the non-compliant adhesives described above.

In accordance with one or more still further alternative embodiments ofthe present invention, substrate 3020 and socket interposer 3050 ofstructure 3000 may be fabricated as a single layer. In accordance withone or more such still further alternative embodiments, theabove-described assembly procedure would be modified so that the Pogopins are inserted into the vias in compliant adhesive layer 3040 beforesubstrate 3020 is placed over compliant adhesive layer 3040. Inaddition, in accordance with one or more still further alternativeembodiments, clamp 3060 may be connected directly to Probe Card 3070. Inaccordance with such one or more still further alternative embodiments,socket interposer 3050 (or substrate 3020 if substrate 3020 and socketinterposer 3050 are fabricated as a single layer) may either beconnected separately to Probe Card 3070, or be held down by clamp 3060.

One or more of the substrates described above have contactors on oneside to contact I/O on an IC, for example, an IC on a wafer (bumped ornot), which contactors are formed of posts and/or bumps. However, itshould be understood that one or more of the above-described embodimentsinclude substrates wherein the contactors are formed of pads. Such padcontactors are useful, for example, for testing ICs on wafers havingbumped I/O.

Although various embodiments that incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

1. A structure useful for testing circuits that comprises: a substratehaving contactors on a first side and pads on a second side; a cardhaving pads on a first side; and interconnectors that electricallyconnect the pads on the second side of the substrate with the pads onthe card, wherein at least one of the interconnectors includes at leasta portion that does not melt at temperatures in a range from about 183°C. to about 230° C., and the distance between the substrate and the cardis determined by a dimension of the at least a portion.
 2. The structureof claim 1, wherein the interconnectors are metal balls.
 3. Thestructure of claim 2, wherein at least one of the interconnectors is oneof: a solid Cu ball, a solid Indium alloy ball, and a solid high leadsolder ball.
 4. The structure of claim 1, wherein at least one of theinterconnectors is a ceramic ball, wherein the ceramic is embedded witha conducting material.
 5. The structure of claim 4, wherein theconducting material comprises one or more of: gold, copper, silver,nickel, and an indium alloy.
 6. The structure of claim 1, furthercomprising an interconnector alignment film, wherein the interconnectorsare partially disposed in vias in the interconnector alignment film. 7.The structure of claim 6, wherein the dimension of the at least aportion is larger than a thickness of the interconnector alignment film.8. The structure of claim 1, wherein the substrate comprises one of: arigid substrate, a flex substrate, a semi-flex substrate, a siliconsubstrate, and a glass substrate.
 9. The structure of claim 1, whereinthe card is a Probe Card, and wherein the structure further comprises astiffening mechanism affixed to a second side of the card.
 10. Thestructure of claim 9, wherein the stiffening mechanism comprises a ringstructure.
 11. The structure of claim 10, wherein the ring structurecomprises one or more of: radial arms, struts, and ribs.
 12. Thestructure of claim 1, wherein: (a) the substrate is a flexiblesubstrate; (b) the contactors are disposed in an area on the first sideof the substrate; and (c) the pads on the substrate are disposed outsideof a projection of the area to the second side of the substrate.